I. Field
The field of the present invention relates to devices and methods for generating light, and more particularly to electrodeless plasma lamps.
II. Background
Electrodeless plasma lamps may be used to provide point-like, bright, white light sources. Because electrodes are not used, they may have longer useful lifetimes than other lamps. Some plasma lamps direct microwave energy into an air cavity, with the air cavity enclosing a bulb containing a mixture of substances that can ignite, form a plasma, and emit light. However, for many applications, light sources that are brighter, smaller, less expensive, more reliable, and have longer useful lifetimes are desired.
Plasma lamps have been proposed that use a dielectric waveguide body to reduce the size of the lamp. See, for example, U.S. Pat. No. 6,737,809 B2 and U.S. Pat. Pub. 2003/0178943. An example lamp of this type may use a solid dielectric waveguide body in the shape of a rectangular prism or cylinder such as shown in FIGS. 1A and 1B, respectively. An amplifier circuit (AC1, AC2) may be used to provide power to the waveguide body (WB1, WB2) to excite a plasma in a bulb (PB1, PB2) positioned within a lamp chamber (LC1, LC2) in the waveguide body.
It may be desirable to reduce the operating frequency for certain applications, so as to reduce the cost of the associated lamp electronics. Because of the wide availability and relatively low cost of parts, operation in the 900 MHz band commonly used for consumer electronics is particularly desirable. Another band of interest is around 2 GHz which in recent years has been widely utilized for state-of-the-art consumer electronics.
One way of reducing frequency is to use materials with a high dielectric constant. However, many such materials suffer from both low thermal conductivity and poor resistance to heat-induced stress, making them poorly suited for a plasma lamp waveguide body. Moreover, some high dielectric constant materials suffer large changes in dielectric constant over the operational temperature range of a plasma lamp.
What is desired are improved plasma lamp configurations, and methods therefor, which can operate at the low end of the microwave frequency range without incurring the size penalty caused by lowering frequency, and which facilitate adjustment of resonant mode frequencies within a selected band. What is also desired are improved plasma lamp configurations, and methods therefor, which allow for a reduced size to be used for operation at a desired frequency. What is also desired are improved bulb and lamp configurations and methods for providing high brightness. What is also desired are improved configurations and methods for ignition, power control and thermal management.